1. Field of the Invention
The present invention relates to the field of command and control of the internal combustion engines of motor vehicles turbocharged by means of a turbocharger. Command and control is the technique for managing an internal combustion engine with all of its sensors and actuators. All the laws of command and control and the parameters for characterizing an engine are contained in a computer called the “electronic control unit” or ECU.
2. Dissussion of the Background
The invention proposes a dynamic method for estimating, with the aid of an air flow meter, the flow rate of cool air supplied to an engine, notably a diesel engine, provided with two exhaust gas recirculation (EGR) circuits. One of the circuits is called the “low-pressure circuit” or LP circuit and the other is called the “high-pressure circuit” or HP circuit.
Currently, the tightening of the standards governing the emissions of pollutant gases at the exhaust of a vehicle requires a considerable reduction in nitrogen oxide emissions. The search for technical solutions making it possible to reduce these emissions has therefore become an issue for automobile manufacturers.
The engine considered in the present invention comprises an engine block furnished with cylinders, an intake manifold for taking in cool oxidant and an exhaust manifold for the burnt gases. The branches of the intake and exhaust manifolds are connected to each of the cylinders.
A turbocharger is situated at the outlet and at the inlet of the engine block. The turbocharger consists of a turbine placed at the outlet of the exhaust manifold of the engine and a compressor placed at the inlet of the intake manifold of the engine. The turbine set in motion by the hot gases originating from the combustion drives the compressor so that it compresses cool air also called intake gas, this cool air moving in the intake manifold of the engine in order to supply, via a heat exchanger device, the combustion chamber of each of the cylinders for the purpose of a combustion of a subsequent operating cycle. In this manner, the work supplied by the exhaust gases is transmitted to the intake gases. The cool air is brought to the turbine of the turbocharger via an air filter. The exhaust gases are discharged via a particle filter.
The particle filter makes it possible to reduce the quantity of particles discharged into the atmosphere. It consists of a set of microchannels in which a large proportion of the particles are trapped. When the filter is full of particles, the filter must be emptied by burning of the particles. This phase is called regeneration. Regeneration can be obtained either by a heating device, or by specific adjustments of the engine.
The quantity of nitrogen oxides produced by a diesel engine is linked to a great extent to the composition of the reactant mixture in air, in fuel and to the presence of inert gases in the engine cylinders. These inert gases play no part in the combustion and come from a circuit diverting a portion of the exhaust gases to the intake circuit. The circuit that allows the recirculation of the exhaust gases is called the EGR circuit. EGR is provided by placing the exhaust circuit in communication with the intake circuit via a passageway section the dimension of which is regulated by a valve called the EGR valve.
The HP EGR circuit is called “high pressure” because it is inside the turbocharging circuit. Specifically, a bypass duct makes the exhaust manifold communicate before the turbine of the turbocharger with the intake manifold after the turbocharger compressor via a cooling device. This duct is furnished with a valve for regulating the flow rate called the HP EGR valve which makes it possible to regulate the dimension of the flow rate. An intake butterfly valve is situated downstream of the heat exchange device and upstream of the connection of the bypass duct with the intake manifold in order to increase the pressure difference in the HP EGR circuit and hence increase the rate of recycled exhaust gases, or EGR rate, recycled by the HP EGR circuit. This circuit is used on all diesel engines meeting the EURO IV clean air standard.
The LP EGR circuit is called “low pressure” because it is outside the turbocharging circuit. Specifically, a bypass duct makes the exhaust circuit downstream of the particle filter communicate with the cool air intake circuit upstream of the turbocharger turbine via a cooling device. This duct is furnished with a flow-rate regulating valve called the LP EGR valve which makes it possible to regulate the dimension of the duct. An exhaust butterfly valve is situated downstream of the particle filter and of the connection of the bypass duct with the exhaust circuit in order to increase the pressure difference in the HP EGR circuit and hence to increase the LP EGR rate.
All of the LP and HP EGR gases make it possible to lower the quantity of nitrogen oxides but risk increasing the smoke if the EGR rate is too high. It is therefore fundamental to compute the exact quantity necessary of total HP and LP EGR gas. Moreover, by modulating the proportion of hot LP EGR gases and of cold LP EGR gases, the two EGR circuits make it possible to control the thermics of the gases taken into the engine in order to reduce the hydrocarbon and carbon monoxide emissions and to control the fuel autoignition delay time.
The cool air flow rate information makes it possible to control, on the one hand, the total HP and LP EGR flow rate by regulating the HP EGR valve, the LP EGR valve, the intake butterfly valve and the exhaust butterfly valve and, on the other hand, the cool air flow rate to a setpoint contained in the ECU. It also makes it possible to limit the quantity of fuel injected into the engine in order to prevent too high particle emissions.
When the driver wants maximum power from the engine, on acceleration, the “foot to the floor” position of the accelerator pedal is converted by the ECU into a fuel flow rate setpoint and the HP and LP EGR valves are closed. This fuel flow rate setpoint is limited in transient by a threshold that is a function of the cool air flow rate and of the engine speed. This device makes it possible to limit the particles present in the exhaust gases of the engine during the transients and limits the filling speed of the particle filter. This limitation is called the “smoke limitation”. If the flow rate value supplied by the flow meter is used directly by the smoke limitation, no account is taken of the time for emptying the HP and LP EGR gas intake circuit. Consequently, it is necessary to have a cool air flow rate value at the engine inlet in order to correctly limit the smoke in transient.
In order to reduce the pollutant emissions, it is necessary to precisely control the total EGR rate at the engine inlet. This control is carried out mainly with the aid of the cool air flow rate measurement. However, since this measurement is taken upstream of the engine intake circuit, it does not take account of the dynamics of this cool air flow rate. Consequently, it is also necessary to have a cool air flow rate value at the engine inlet in order to correctly limit the total EGR smoke at the engine inlet.
Knowing the cool air flow rate information is therefore fundamental.
Solutions exist but are not sufficiently satisfactory.
Patent application FR 2 910 929 proposes an estimation of the air flow rate entering an engine fitted with two circuits, HP and LP EGR circuits, without the aid of a flow meter. However, this solution is clumsy to apply. It is also sensitive and not very robust with respect to the dispersions over all of the sensors used for this estimation.
Another solution is described in patent FR 2 789 731 in which a method is proposed for estimating the cool air flow rate based on the engine speed, the pressure and the temperature of air in the intake manifold and an estimate of the HP EGR flow rate with the aid of the position of the valve and of applying the formula of Barré de Saint-Venant. However, this solution is no longer valid in the presence of a variable backpressure at the exhaust, for example, when a variable-geometry turbocharger or a particle filter is used.
Patent application FR 2 824 596 offers an improvement on the solution proposed in patent application FR 2 789 731 by taking account of the pressure difference at the limits of the HP EGR valve when the formula of Barré de Saint-Venant is applied. The main drawback is the great sensitivity of the model when the pressures at the limits of the EGR valve are very similar, which represents most of the operating points.
Patent applications FR 2 833 648, FR 2 833 649 and EP1 024 262 A2 propose a method for estimating the HP EGR flow rate by using the formula of Barré de Saint-Venant followed by the cool air flow rate by deducting the HP EGR flow rate from the total quantity accepted. The resulting cool air flow rate is filtered by the use of a monitoring element checking the pressure in the manifold. The same drawback is found as for patent application FR 2 824 596.
U.S. Pat. Nos. 5,270,935 and 5,273,019 describe a method for estimating the air flow rate entering the engine by making a comparison between a pressure value in the manifold estimated by a parametric model and the value of this measured pressure. The difference between the measurement and the estimate of the pressure in the manifold is combined with a set of correction coefficients optimized to recompute both the pressure in the manifold and the air flow rate.
U.S. Pat. No. 5,273,019 makes it possible to determine the incoming HP EGR flow rate by estimating the partial air pressure in the manifold using the same method as the patents above. The solutions proposed by these patents are difficult to apply in industrial computers because, on the one hand, of the difficulty of their integration associated with the required memory and, on the other hand, with the considerable computation time necessary.
No element of this prior art is compatible with an engine fitted with two EGR circuits, one LP and the other HP, and the use of an air flow meter.
The object of the present invention is to alleviate one or more drawbacks of the prior art and to propose a dynamic method for estimating the cool air flow rate entering an engine fitted with two EGR circuits, one being an HP EGR and the other an LP EGR circuit, with the aid of an air flow meter situated in the intake circuit upstream of the turbocharger and of the connection of the bypass duct of the LP EGR circuit.
According to the invention, the method for estimating the dynamic flow rate of cool air entering an engine, particularly a diesel engine, turbocharged by a turbocharger, fitted at least with an intake manifold, with an exchanger, with an air filter, with an HP EGR circuit, with an LP EGR circuit, with an intake butterfly valve control, with an exhaust butterfly valve control, with a flow meter, with a pressure sensor and a temperature sensor connected to an ECU is characterized in that it comprises the following steps:                measurement of the temperature after the exchanger by the temperature sensor, of the pressure in the manifold by the pressure sensor and of the flow rate of cool air by the flow meter,        computation by the ECU of the engine flow rate based on the measurement of the temperature after the exchanger and of the pressure in the manifold,        computation by the ECU of the mass of gas between the flow meter and the inlet of the manifold based on the measurement of the temperature after the exchanger and of the pressure in the manifold,        computation by the ECU of the mass of gas in the manifold based on the measurement of the temperature after the exchanger and of the pressure in the manifold,        measurement or estimation of the HP EGR flow rate,        computation by the ECU of the gas flow rate in the manifold based on the engine flow rate and on the mass of gas in the manifold;        estimation by the ECU of the rate of LP EGR at the inlet of the manifold based on the mass of gas between the flow meter and the manifold inlet, on the flow rate of gas in the manifold and on the cool air flow rate measured by the flow meter;        computation by the ECU of the mass of air between the flow meter and the manifold inlet based on the LP EGR rate at the inlet of the manifold and on the flow rate of cool air measured by the flow meter;        estimation by the ECU of the EGR rate at the engine inlet based on the mass of air between the flow meter and the inlet of the manifold, on the mass in the manifold and on the flow rate of cool air measured by the flow meter,        estimation by the ECU of the dynamic engine air flow rate based on the engine flow rate and on the EGR rate at the engine inlet.        
According to another particular feature, the cool air flow rate is estimated by taking account of the following items of information:                detection of the aperture of the intake butterfly valve;        temperature in the whole intake circuit considered to be equal to the temperature Tape after the exchanger;        mass of gas between the flow meter and the inlet of the manifold estimated by an algorithm using the following formula:        
            M      cool        =                            P          coll                ·                  V          cool                            R        ·                  T          ape                      ,where Pcoll=pressure measured in the manifold,
Vcool=volume of gas between the flow meter and the manifold inlet,
Tape=temperature measured after the exchanger and R is the individual constant of the air;                mass of gas in the manifold estimated by an algorithm using the following formula        
      M    coll    =                    P        coll            ·              V        coll                    R      ·              T        ape            where Vcoll=volume of the manifold;                the HP EGR flow rate QEGR—HP—coll entering the manifold is provided by the ECU by measurement or estimation.        
According to another particular feature, the estimation method is characterized in that it uses the following operations:                determination of the flow rate Qmot of gas that has entered the engine        
      Q    mot    =      3600    ×          [                                    P            coll                                R            ·                          T              ape                                      ⁢                              V            cyl                    2                ⁢                  N          60                ⁢                              η            r                    ⁡                      (                          N              ,                                                P                  coll                                                  R                  ·                                      T                    ape                                                                        )                              ]      where Vcyl=cubic inch displacement of the engine, N=engine rotation speed, Pcoll=pressure measured in the manifold, Tape=temperature measured after the exchanger, ηr=volumetric efficiency of the engine and R=individual constant of the air                computation by the ECU of the EGR rate in the engine        
      τ          EGR      ⁢                          ⁢              _        ⁢        mot              =                    M                  EGR          ⁢                                          ⁢                      _            ⁢            coll                                                M                      EGR            ⁢                                                  ⁢                          _              ⁢              coll                                      +                  M                      air            ⁢                                                  ⁢                          _              ⁢              coll                                            =                  Q                  EGR          ⁢                                          ⁢                      _            ⁢            mot                                                Q                      EGR            ⁢                                                  ⁢                          _              ⁢              mot                                      +                  Q                      air            ⁢                                                  ⁢                          _              ⁢              mot                                          where TEGR—mot=EGR rate at the engine inlet, MEGR—coll=mass of the HP EGR gases in the volume of the manifold, Mair—coll=mass of the air in the volume of the manifold, QEGR—mot=HP and LP EGR flow rate entering the engine, Qair—mot=air flow rate entering the engine                computation by the ECU of the LP EGR rate at the manifold inlet        
      τ          EGR_BP      ⁢      _coll        =                    M                  EGR_BP          ⁢          _cool                                      M                      EGR_BP            ⁢            _cool                          +                  M          air_cool                      =                  Q                  EGR_BP          ⁢          _coll                                      Q                      EGR_BP            ⁢            _coll                          +                  Q          air_coll                    where τEGR—BP—Coll=LP EGR rate at the manifold inlet, MEGR—BP—cool=mass of the LP EGR gases between the flow meter and the manifold inlet, Mair—cool=mass of the air between the flow meter and the manifold inlet, QEGR—BP—coll=LP EGR flow rate entering the manifold, Qair—coll=air flow rate entering the manifold,                control of the butterfly valves in order to retain the mass in the manifold        
  {                                                                        ⅆ                                  M                  air_coll                                                            ⅆ                t                                      =                                          Q                air_coll                            -                              Q                air_mot                                                                                                                    ⅆ                                  M                  EGR_coll                                                            ⅆ                t                                      =                                          Q                                  EGR_coll                  ⁢                                                                                                    -                              Q                EGR_mot                                                             
and determination of the latter by applying a computation algorithm using the following equation
            ⅆ              M        coll                    ⅆ      t        =            Q      air_coll        +          Q      EGR_coll        -          Q      mot      where Qmot=Qair—mot+QEGR—mot and Mcoll=Mair—coll+MEGR—coll.                control of the butterfly valves to retain the mass in the exchanger        
  {                                                                        ⅆ                                  M                  air_cool                                                            ⅆ                t                                      =                                          Q                débitmètre                            -                              Q                air_coll                                                                                                                    ⅆ                                  M                                      EGR_BP                    ⁢                    _cool                                                                              ⅆ                t                                      =                                          Q                                                      EGR_BP                    ⁢                    _dyn                                    ⁢                                                                                                    -                              Q                                  EGR_BP                  ⁢                  _coll                                                                             
and determination of the latter by the application of a computation algorithm using the following equation
            ⅆ              M        cool                    ⅆ      t        =            Q      débitmètre        +          Q              EGR_BP        ⁢        _dyn              -          Q      coll      where Qcoll=Qair—coll+QEGR—BP—coll and Mcool=Mair—cool+MEGR—BP—cool 
based on which the ECU estimates the LP EGR and engine EGR rates:                by applying a differential equation for estimating the LP EGR rate at the manifold inlet        
            ⅆ                        τ          ^                          EGR_BP          ⁢          _coll                            ⅆ      t        =            1              M        cool              ·          [                                    (                          1              -                                                τ                  ^                                                                      EGR                    ⁢                    _                    ⁢                    BP                                    ⁢                                      _                    ⁢                    coll                                                                        )                    ·                      (                                          Q                coll                            +                                                ⅆ                                      M                    cool                                                                    ⅆ                  t                                                      )                          -                  Q          débitmètre                    ]                      and a differential equation for estimating the engine EGR rate        
            ⅆ                        τ          ^                          EGR_mo          ⁢          t                            ⅆ      t        =            1              M        coll              ·          [                                    (                          1              -                                                τ                  ^                                EGR_mot                                      )                    ·                      (                                          Q                mot                            +                                                ⅆ                                      M                    coll                                                                    ⅆ                  t                                                      )                          +                              ⅆ                          M              air_cool                                            ⅆ            t                          -                  Q          débitmètre                    ]      
According to one embodiment, the differential equations in EGR rate are resolved discretely:
                    τ        ^                              EGR          ⁢          _          ⁢          BP                ⁢                  _          ⁢          coll                      =                  1                  M          cool                    ·              ∑                              [                                                            (                                      1                    -                                                                  τ                        ^                                                                                              EGR                          ⁢                          _                          ⁢                          BP                                                ⁢                                                                              _                            ⁢                            coll                                                                                n                            -                            1                                                                                                                                )                                ·                                  (                                                            Q                      coll                                        +                                                                  ⅆ                                                  M                          cool                                                                                            ⅆ                        t                                                                              )                                            -                              Q                débitmètre                                      ]                    ⁢                                          ⁢          and                                        τ        ^            EGR_mot        =                  1                  M          coll                    ·              ∑                  [                                                    (                                  1                  -                                                            τ                      ^                                                                                      EGR                        ⁢                        _                        ⁢                        mot                                                                    n                        -                        1                                                                                            )                            ·                              (                                                      Q                    mot                                    +                                                            ⅆ                                              M                        coll                                                                                    ⅆ                      t                                                                      )                                      +                                          ⅆ                                  M                                      air                    ⁢                    _                    ⁢                    cool                                                                              ⅆ                t                                      -                          Q              débitmètre                                ]                    
According to one embodiment, with no HP EGR circuit, the method for estimating the cool air flow rate entering an engine, notably a diesel engine, turbocharged by a turbocharger, fitted at least with an LP EGR circuit, a flow meter, an intake manifold, an exchanger, an air filter, an intake butterfly valve control, an exhaust butterfly valve control, a pressure sensor and a temperature sensor connected to an ECU is characterized in that it comprises the following steps:                measurement of the temperature after the exchanger by the temperature sensor, of the pressure in the manifold by the pressure sensor and of the flow rate of cool air by the flow meter,        computation by the ECU of the engine flow rate based on the measurement of temperature after the exchanger and of the pressure in the manifold,        computation by the ECU of the mass of gas in the intake based on the measurement of temperature after the exchanger and of the pressure in the manifold,        estimation by the ECU of the LP EGR rate in the engine based on the cool air flow rate measured by the flow meter, on the engine flow rate and on the mass of gas in the intake,        estimation by the ECU of the engine air flow rate based on the LP EGR rate and on the engine flow rate.        
According to one embodiment with no HP EGR circuit, the cool air flow rate is estimated taking account of the following information:                detection of the aperture of the intake butterfly valve;        temperature in the whole intake circuit considered to be equal to the temperature Tape after the exchanger;        mass of gas between the flow meter and the engine inlet estimated by an algorithm using the following formula:        
            M      adm        =                            P          coll                ·                  V          adm                            R        ·                  T          ape                      ,where Pcoll=pressure measured in the manifold,                vadm=volume of gas between the flow meter and the engine inlet,        
Tape=temperature measured after the exchanger and R the individual constant of the air.
According to one embodiment with no HP EGR circuit, the estimation method is characterized in that it applies the following operations:                determination of the flow rate Qmot of gas that has entered the engine        
      Q    mot    =            N      120        ·                  P        coll                    R        ·                  T          ape                      ·                  η        r            ⁡              (                                            P              coll                                      R              ·                              T                ape                                              ,          N                )              ·          V      cyl      where Vcyl=displacement of the engine, N=rotation speed of the engine, Pcoll=pressure measured in the manifold, Tape=temperature measured after the exchanger, ηr=volumetric efficiency of the engine and R=individual constant of the air                estimation by the ECU of the LP EGR rate at the engine inlet        
            ⅆ                        τ          ^                                      EGR            ⁢            _            ⁢            BP                    ⁢                      _            ⁢            mot                                      ⅆ      t        =            1              M        cool              ·          [                                    (                          1              -                                                τ                  ^                                                  EGR_BP                  ⁢                  _coll                                                      )                    ·                      (                                          Q                mot                            +                                                ⅆ                                      M                    adm                                                                    ⅆ                  t                                                      )                          -                  Q          débitmètre                    ]      
According to one embodiment with no HP EGR, the differential equation in estimated EGR rate is resolved discretely:
            τ      ^                      EGR        ⁢        _        ⁢        BP            ⁢              _        ⁢        mot              =            1              M        cool              ⁢          ∑              ·                  [                                                    (                                  1                  -                                                            τ                      ^                                                                                      EGR                        ⁢                        _                        ⁢                        BP                                            ⁢                                                                        _                          ⁢                          mot                                                                          n                          -                          1                                                                                                                    )                            ·                              (                                                      Q                    mot                                    +                                                            ⅆ                                              M                        adm                                                                                    ⅆ                      t                                                                      )                                      -                          Q              débitmètre                                ]                    